Systems and methods for detecting air filter fouling in a climate control system

ABSTRACT

Methods and related systems for operating a climate control system for an indoor space are disclosed. In an embodiment, the method includes increasing a speed of a fan of the climate control system, and determining a first fitted external static pressure (ESP) function from a first plurality of airflow values and a first plurality of ESP values. Additionally, the method includes obtaining a baseline ESP from the first fitted ESP function, and determining a second fitted ESP function from a second plurality of airflow values and a second plurality of ESP values collected at least one week after the first plurality of airflow values and the first plurality of ESP values are collected. Further, the method includes comparing the first calculated ESP obtained from the second fitted ESP function to the baseline ESP to determine a condition of an air filter of the climate control system.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

Climate control systems, such as heating, ventilation, and/or airconditioning (HVAC) systems may generally be used in residential and/orcommercial areas for heating and/or cooling to create comfortabletemperatures inside those areas. Some climate control systems may besplit-type heat pump systems. These systems typically have an indoor airhandling unit and an outdoor unit, which are capable of cooling acomfort zone by operating in a cooling mode for transferring heat from acomfort zone to an ambient zone using a refrigeration cycle. Thesesystems are also generally capable of reversing the direction ofrefrigerant flow through the components of the climate control system sothat heat is transferred from the ambient zone to the comfort zone,thereby heating the comfort zone. Climate control systems often includean air filer or cleaner to capture particulates and other contaminates.These particulates and other contaminates gradually accumulate on theair filter or cleaner of the climate control system during the operationof the climate control system, leading to the eventual “fouling” orclogging of the air filter. A fouled air filter may result in asubstantially high external static pressure (ESP) across an aircirculation path of the climate control system, including across the airfilter, reducing the effectiveness of the climate control system andincreasing a power usage of a motor of the climate control system neededto overcome the increased ESP.

BRIEF SUMMARY

Some embodiments disclosed herein are directed to a method of operatinga climate control system for an indoor space. In an embodiment, themethod includes increasing, from idle, a speed of an indoor fan of theclimate control system to increase an airflow through the indoor space,and determining a first fitted external static pressure (ESP) functionfrom a first plurality of airflow values and a first plurality of ESPvalues. In addition, the method includes obtaining a baseline ESP valueof the climate control system from the first fitted ESP function, anddetermining a second fitted ESP function from a second plurality ofairflow values and a second plurality of ESP values collected at leastone week after the first plurality of airflow values and the firstplurality of ESP values are collected. Further, the method includesobtaining a first calculated ESP value of the climate control systemfrom the second fitted ESP function, and comparing the first calculatedESP value to the baseline ESP value to determine a condition of an airfilter of the climate control system.

Other embodiments disclosed herein are directed to a climate controlsystem for an indoor space. In an embodiment, the climate control systemincludes an indoor fan configured to produce an airflow through theindoor space, and an air filter configured to filter contaminants in theairflow produced by the indoor fan. In addition, the climate controlsystem includes a controller to be coupled to the indoor fan. Thecontroller is configured to increase, from idle, a speed of the indoorfan of the climate control system to increase the airflow through theindoor space, and determine a first fitted external static pressure(ESP) function from a first plurality of airflow values and a firstplurality of ESP values. In addition, the controller is configured toobtain a baseline ESP value of the climate control system from the firstfitted ESP function, and determine a second fitted ESP function from asecond plurality of airflow values and a second plurality of ESP valuescollected by the controller at least one week after the first pluralityof airflow values and the first plurality of ESP values are collected bythe controller. Further, the controller is configured to obtain a firstcalculated ESP value of the climate control system from the secondfitted ESP function, and compare the first calculated ESP value to thebaseline ESP value to determine a condition of the air filter of theclimate control system.

Still other embodiments disclosed herein are directed to anon-transitory machine-readable medium including instructions that, whenexecuted by a processor, cause the processor to increase, from idle, aspeed of an indoor fan of the climate control system to increase anairflow through the indoor space, and determine a first fitted externalstatic pressure (ESP) function from a first plurality of airflow valuesand a first plurality of ESP values. In addition, the instructions, whenexecuted by a processor, cause the processor to obtain a baseline ESPvalue of the climate control system from the first fitted ESP function,and determine a second fitted ESP function from a second plurality ofairflow values and a second plurality of ESP values collected by thecontroller at least one week after the first plurality of airflow valuesand the first plurality of ESP values are collected by the controller.Further, the instructions, when executed by a processor, cause theprocessor to obtain a first calculated ESP value of the climate controlsystem from the second fitted ESP value, and compare the firstcalculated ESP value to the baseline ESP value to determine a conditionof an air filter of the climate control system.

Embodiments described herein comprise a combination of features andcharacteristics intended to address various shortcomings associated withcertain prior devices, systems, and methods. The foregoing has outlinedrather broadly the features and technical characteristics of thedisclosed embodiments in order that the detailed description thatfollows may be better understood. The various characteristics andfeatures described above, as well as others, will be readily apparent tothose skilled in the art upon reading the following detaileddescription, and by referring to the accompanying drawings. It should beappreciated that the conception and the specific embodiments disclosedmay be readily utilized as a basis for modifying or designing otherstructures for carrying out the same purposes as the disclosedembodiments. It should also be realized that such equivalentconstructions do not depart from the spirit and scope of the principlesdisclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various exemplary embodiments, referencewill now be made to the accompanying drawings in which:

FIG. 1 is a diagram of a HVAC system configured for operating in acooling mode according to some embodiments;

FIG. 2 is a schematic diagram of an air circulation path of the HVACsystem of FIG. 1 according to an embodiment of the disclosure;

FIG. 3 is a flow chart of a method of determining a condition of an airfilter of a climate control system according to some embodiments;

FIG. 4 is a graph illustrating estimated airflow and ESP of a climatecontrol system according to some embodiments; and

FIG. 5 is a graph illustrating fitted airflow and ESP of a climatecontrol system according to some embodiments.

DETAILED DESCRIPTION

The following discussion is directed to various exemplary embodiments.However, one of ordinary skill in the art will understand that theexamples disclosed herein have broad application, and that thediscussion of any embodiment is meant only to be exemplary of thatembodiment, and not intended to suggest that the scope of thedisclosure, including the claims, is limited to that embodiment.

The drawing figures are not necessarily to scale. Certain features andcomponents herein may be shown exaggerated in scale or in somewhatschematic form and some details of conventional elements may not beshown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection of the two devices,or through an indirect connection that is established via other devices,components, nodes, and connections. In addition, as used herein, theterms “axial” and “axially” generally mean along or parallel to a givenaxis (e.g., central axis of a body or a port), while the terms “radial”and “radially” generally mean perpendicular to the given axis. Forinstance, an axial distance refers to a distance measured along orparallel to the axis, and a radial distance means a distance measuredperpendicular to the axis. Further, when used herein (including in theclaims), the words “about,” “generally,” “substantially,”“approximately,” and the like mean within a range of plus or minus 10%.

As previously described, particulates and other contaminates graduallyaccumulate on an air filter or cleaner of the climate control systemduring the operation of the climate control system, leading to theeventual “fouling” of the air filter that may reduce the effectivenessof the filter for removing contaminants from an air circulation path ofthe climate control system and increase a power usage of a motor of theclimate control system in order to overcome an increased ESP (air flowrestriction) across an air circulation path of the climate controlsystem, including across the fouled or clogged air filter. Some climatecontrol systems may be configured to provide a periodic alert to a userof the climate control system to replace the air filter, where theduration between the periodic alert is a fixed interval. In otherclimate control systems, a run time of a fan of the climate controlsystem may be tracked by a controller of the climate control system andan alert may be provided to the user once a threshold run time for thefan has been exceeded. However, neither the fixed interval and fantracking methods are capable of detecting fouling of the air filter, andthus, the alert provided to the user of the climate control system bythese methods may be too soon—before the air filter has fouled—or toolate—a substantial duration of time after the filter has fouled.Accordingly, embodiments disclosed herein include systems and methodsfor detecting fouling or clogging of an air filter of a climate controlsystem. As will be described in more detail below, use of theembodiments disclosed herein may allow a climate control system toaccurately and timely generate an alert to a user of the control systemto change the air filter.

Referring now to FIG. 1 , a schematic diagram of a climate controlsystem 100 according to some embodiments is shown. In this embodiment,climate control system 100 is a HVAC system, and thus, system 100 may bereferred to herein as HVAC system 100. Most generally, HVAC system 100comprises a heat pump system that may be selectively operated toimplement one or more substantially closed thermodynamic refrigerationcycles to provide a cooling functionality (hereinafter “cooling mode”),a heating functionality (hereinafter “heating mode”), and/or an aircirculation functionality (hereinafter “fan only mode”). The HVAC system100, configured as a heat pump system, generally comprises an indoorunit 102, an outdoor unit 104, and a system controller 106 that maygenerally control operation of the indoor unit 102 and/or the outdoorunit 104.

Indoor unit 102 generally comprises an indoor air handling unitcomprising an indoor heat exchanger 108, an indoor fan 110, an indoormetering device 112, and an indoor controller 124. The indoor heatexchanger 108 may generally be configured to promote heat exchangebetween refrigerant carried within internal tubing of the indoor heatexchanger 108 and an airflow that may contact the indoor heat exchanger108 but that is segregated from the refrigerant. Specifically, indoorheat exchanger 108 may include a coil 109 for channeling the refrigeranttherethrough that segregates the refrigerant from any air flowingthrough indoor heat exchanger 108 during operations. In someembodiments, the indoor heat exchanger 108 may comprise a plate-fin heatexchanger. However, in other embodiments, indoor heat exchanger 108 maycomprise a microchannel heat exchanger and/or any other suitable type ofheat exchanger.

The indoor fan 110 may generally comprise a centrifugal blowercomprising a blower housing, a blower impeller at least partiallydisposed within the blower housing, and a blower motor configured toselectively rotate the blower impeller. The indoor fan 110 may generallybe configured to provide airflow through the indoor unit 102 and/or theindoor heat exchanger 108 (specifically across or over the coil 109) topromote heat transfer between the airflow and a refrigerant flowingthrough the coil 109 of the indoor heat exchanger 108. The indoor fan110 may also be configured to deliver temperature-conditioned air fromthe indoor unit 102 to one or more areas and/or zones of an indoorspace. The indoor fan 110 may generally comprise a mixed-flow fan and/orany other suitable type of fan. The indoor fan 110 may generally beconfigured as a modulating and/or variable speed fan capable of beingoperated at many speeds over one or more ranges of speeds. In otherembodiments, the indoor fan 110 may be configured as a multiple speedfan capable of being operated at a plurality of operating speeds byselectively electrically powering different ones of multipleelectromagnetic windings of a motor of the indoor fan 110.

The indoor metering device 112 may generally comprise anelectronically-controlled motor-driven electronic expansion valve (EEV).In some embodiments, however, the indoor metering device 112 maycomprise a thermostatic expansion valve, a capillary tube assembly,and/or any other suitable metering device. In some embodiments, whilethe indoor metering device 112 may be configured to meter the volumeand/or flow rate of refrigerant through the indoor metering device 112,the indoor metering device 112 may also comprise and/or be associatedwith a refrigerant check valve and/or refrigerant bypass configurationwhen the direction of refrigerant flow through the indoor meteringdevice 112 is such that the indoor metering device 112 is not intendedto meter or otherwise substantially restrict flow of the refrigerantthrough the indoor metering device 112.

Outdoor unit 104 generally comprises an outdoor heat exchanger 114, acompressor 116, an outdoor fan 118, an outdoor metering device 120, areversing valve 122, and an outdoor controller 126. In some embodiments,the outdoor unit 104 may also comprise a plurality of temperaturesensors for measuring the temperature of the outdoor heat exchanger 114,the compressor 116, and/or the outdoor ambient temperature. The outdoorheat exchanger 114 may generally be configured to promote heat transferbetween a refrigerant carried within internal passages of the outdoorheat exchanger 114 and an airflow that contacts the outdoor heatexchanger 114 but that is segregated from the refrigerant. In someembodiments, outdoor heat exchanger 114 may comprise a plate-fin heatexchanger. However, in other embodiments, outdoor heat exchanger 114 maycomprise a spine-fin heat exchanger, a microchannel heat exchanger, orany other suitable type of heat exchanger. While not specifically shown,it should be appreciated that outdoor heat exchanger 114 may include acoil similar to coil 109 previously described above for indoor heatexchanger 108.

The compressor 116 may generally comprise a variable speed scroll-typecompressor that may generally be configured to selectively pumprefrigerant at a plurality of mass flow rates through the indoor unit102, the outdoor unit 104, and/or between the indoor unit 102 and theoutdoor unit 104. In some embodiments, the compressor 116 may comprise arotary type compressor configured to selectively pump refrigerant at aplurality of mass flow rates. In some embodiments, however, thecompressor 116 may comprise a modulating compressor that is capable ofoperation over a plurality of speed ranges, a reciprocating-typecompressor, a single speed compressor, and/or any other suitablerefrigerant compressor and/or refrigerant pump. In some embodiments, thecompressor 116 may be controlled by a compressor drive controller 144,also referred to as a compressor drive and/or a compressor drive system.

The outdoor fan 118 may generally comprise an axial fan comprising a fanblade assembly and fan motor configured to selectively rotate the fanblade assembly. The outdoor fan 118 may generally be configured toprovide airflow through the outdoor unit 104 and/or the outdoor heatexchanger 114 to promote heat transfer between the airflow and arefrigerant flowing through the indoor heat exchanger 108. The outdoorfan 118 may generally be configured as a modulating and/or variablespeed fan capable of being operated at a plurality of speeds over aplurality of speed ranges. In other embodiments, the outdoor fan 118 maycomprise a mixed-flow fan, a centrifugal blower, and/or any othersuitable type of fan and/or blower, such as a multiple speed fan capableof being operated at a plurality of operating speeds by selectivelyelectrically powering different multiple electromagnetic windings of amotor of the outdoor fan 118. In yet other embodiments, the outdoor fan118 may be a single speed fan. Further, in other embodiments, theoutdoor fan 118 may comprise a mixed-flow fan, a centrifugal blower,and/or any other suitable type of fan and/or blower.

The outdoor metering device 120 may generally comprise a thermostaticexpansion valve. In some embodiments, however, the outdoor meteringdevice 120 may comprise an electronically-controlled motor driven EEVsimilar to indoor metering device 112, a capillary tube assembly, and/orany other suitable metering device. In some embodiments, while theoutdoor metering device 120 may be configured to meter the volume and/orflow rate of refrigerant through the outdoor metering device 120, theoutdoor metering device 120 may also comprise and/or be associated witha refrigerant check valve and/or refrigerant bypass configuration whenthe direction of refrigerant flow through the outdoor metering device120 is such that the outdoor metering device 120 is not intended tometer or otherwise substantially restrict flow of the refrigerantthrough the outdoor metering device 120.

The reversing valve 122 may generally comprise a four-way reversingvalve. The reversing valve 122 may also comprise an electrical solenoid,relay, and/or other device configured to selectively move a component ofthe reversing valve 122 between operational positions to alter the flowpath of refrigerant through the reversing valve 122 and consequently theHVAC system 100. Additionally, the reversing valve 122 may also beselectively controlled by the system controller 106 and/or an outdoorcontroller 126.

The system controller 106 may generally be configured to communicatewith an indoor controller 124 of the indoor unit 102, an outdoorcontroller 126 of the outdoor unit 104, and/or other components of theHVAC system 100. In some embodiments, the system controller 106 may beconfigured to control operation of the indoor unit 102 and/or theoutdoor unit 104. In some embodiments, the system controller 106 may beconfigured to monitor and/or communicate, directly or indirectly, with aplurality of sensors associated with components of the indoor unit 102,the outdoor unit 104, etc. The sensors may measure or detect a varietyof parameters, such as, for example, pressure, temperature, and flowrate of the refrigerant as well as pressure and temperature of othercomponents or fluids of or associated with HVAC system 100. In someembodiments, the HVAC system 100 may include a sensor (or plurality ofsensors) for sensing or detecting the ambient outdoor temperature.Additionally, in some embodiments, the system controller 106 maycomprise a temperature sensor and/or may further be configured tocontrol heating and/or cooling of zones associated with the HVAC system100 (e.g., within the indoor space). In some embodiments, the systemcontroller 106 may be configured as a thermostat, having a temperaturesensor and a user interface, for controlling the supply of conditionedair to zones associated within the HVAC system 100.

The system controller 106 may also be in communication with aninput/output (I/O) unit 107 (e.g., a graphical user interface, atouchscreen interface, or the like) for displaying information and forreceiving user inputs. The I/O unit 107 may display information relatedto the operation of the HVAC system 100 (e.g., from system controller106) and may receive user inputs related to operation of the HVAC system100. During operations, I/O unit 107 may communicate received userinputs to the system controller 106, which may then execute control ofHVAC system 100 accordingly. Communication between the I/O unit 107 andsystem controller 106 may be wired, wireless, or a combination thereof.In some embodiments, the I/O unit 107 may further be operable to displayinformation and receive user inputs tangentially and/or unrelated tooperation of the HVAC system 100. In some embodiments, however, the I/Ounit 107 may not comprise a display and may derive all information frominputs from remote sensors and remote configuration tools (e.g., remotecomputers, servers, smartphones, tablets, etc.). In some embodiments,system controller 106 may receive user inputs from remote configurationtools, and may further communicate information relating to HVAC system100 to I/O unit 107. In these embodiments, system controller 106 may ormay not also receive user inputs via I/O unit 107.

In some embodiments, the system controller 106 may be configured forselective bidirectional communication over a communication bus 128. Insome embodiments, portions of the communication bus 128 may comprise athree-wire connection suitable for communicating messages between thesystem controller 106 and one or more of the HVAC system 100 componentsconfigured for interfacing with the communication bus 128. Stillfurther, the system controller 106 may be configured to selectivelycommunicate with HVAC system 100 components and/or any other device 130via a communication network 132. In some embodiments, the communicationnetwork 132 may comprise a telephone network, and the other device 130may comprise a telephone. In some embodiments, the communication network132 may comprise the Internet, and the other device 130 may comprise asmartphone and/or other Internet-enabled mobile telecommunicationdevice. In other embodiments, the communication network 132 may alsocomprise a remote server.

The indoor controller 124 may be carried by the indoor unit 102 and maygenerally be configured to receive information inputs, transmitinformation outputs, and/or otherwise communicate with the systemcontroller 106, the outdoor controller 126, and/or any other device 130via the communication bus 128 and/or any other suitable medium ofcommunication. In some embodiments, the indoor controller 124 may beconfigured to communicate with an indoor personality module 134 that maycomprise information related to the identification and/or operation ofthe indoor unit 102. In some embodiments, the indoor controller 124 maybe configured to receive information related to a speed of the indoorfan 110, transmit a control output to an electric heat relay, transmitinformation regarding an indoor fan 110 volumetric flow-rate,communicate with and/or otherwise affect control over an air cleaner orfilter 136, and communicate with an indoor EEV controller 138. In someembodiments, the indoor controller 124 may be configured to communicatewith an indoor fan controller 142 and/or otherwise affect control overoperation of the indoor fan 110. In some embodiments, the indoorpersonality module 134 may comprise information related to theidentification and/or operation of the indoor unit 102 and/or a positionof the outdoor metering device 120.

The indoor EEV controller 138 may be configured to receive informationregarding temperatures and/or pressures of the refrigerant in the indoorunit 102. More specifically, the indoor EEV controller 138 may beconfigured to receive information regarding temperatures and pressuresof refrigerant entering, exiting, and/or within the indoor heatexchanger 108. Further, the indoor EEV controller 138 may be configuredto communicate with the indoor metering device 112 and/or otherwiseaffect control over the indoor metering device 112. The indoor EEVcontroller 138 may also be configured to communicate with the outdoormetering device 120 and/or otherwise affect control over the outdoormetering device 120.

The outdoor controller 126 may be carried by the outdoor unit 104 andmay be configured to receive information inputs, transmit informationoutputs, and/or otherwise communicate with the system controller 106,the indoor controller 124, and/or any other device 130 via thecommunication bus 128 and/or any other suitable medium of communication.In some embodiments, the outdoor controller 126 may be configured tocommunicate with an outdoor personality module 140 that may compriseinformation related to the identification and/or operation of theoutdoor unit 104. In some embodiments, the outdoor controller 126 may beconfigured to receive information related to an ambient temperatureassociated with the outdoor unit 104, information related to atemperature of the outdoor heat exchanger 114, and/or informationrelated to refrigerant temperatures and/or pressures of refrigerantentering, exiting, and/or within the outdoor heat exchanger 114 and/orthe compressor 116. In some embodiments, the outdoor controller 126 maybe configured to transmit information related to monitoring,communicating with, and/or otherwise affecting control over thecompressor 116, the outdoor fan 118, a solenoid of the reversing valve122, a relay associated with adjusting and/or monitoring a refrigerantcharge of the HVAC system 100, a position of the indoor metering device112, and/or a position of the outdoor metering device 120. The outdoorcontroller 126 may further be configured to communicate with and/orcontrol a compressor drive controller 144 that is configured toelectrically power and/or control the compressor 116.

System controller 106, indoor controller 124, and outdoor controller 126(as well as compressor drive controller 144, indoor fan controller 142,indoor EEV controller 138, etc.) may each comprise any suitable deviceor assembly which is capable of receiving electrical (or other data)signals and transmitting electrical (or other data) signals to otherdevices. In particular, while not specifically shown, system controller106, indoor controller 124, and outdoor controller 126 (as well ascontrollers 138, 142, 144, etc.) may each include a processor and amemory. The processors (e.g., microprocessor, central processing unit,or collection of such processor devices, etc.) may execute machinereadable instructions (e.g., non-transitory machine readable medium)provided on the corresponding memory to provide the processor with allof the functionality described herein. The memory of each controller106, 124, 126 may comprise volatile storage (e.g., random accessmemory), non-volatile storage (e.g., flash storage, read only memory,etc.), or combinations of both volatile and non-volatile storage. Dataconsumed or produced by the machine readable instructions can also bestored on the memory of controllers 106, 124, 126.

During operations, system controller 106 may generally control theoperation of HVAC system 100 through the indoor controller 124 andoutdoor controller 126 (e.g., via communication bus 128). In thedescription below, specific control methods are described (e.g., method300). It should be understood that the features of these describedmethods may be performed (e.g., wholly or partially) by systemcontroller 106, or by one or more of the indoor controller 124, andoutdoor controller 126 as directed by system controller 106. As aresult, the controller or controllers of HVAC system 100 (e.g.,controllers 106, 124, 126, 142, 144, 138, etc.) may include and executemachine-readable instructions (e.g., non-volatile machine readableinstructions) for performing the operations and methods described inmore detail below. In some embodiments, each of the controllers 106,124, 126 may be embodied in a singular control unit, or may be dispersedthroughout the individual controllers 106, 124, 126 as described above.

As shown in FIG. 1 , the HVAC system 100 is configured for operating ina so-called cooling mode in which heat may generally be absorbed byrefrigerant at the indoor heat exchanger 108 and rejected from therefrigerant at the outdoor heat exchanger 114. Starting at thecompressor 116, the compressor 116 may be operated to compressrefrigerant and pump the relatively high temperature and high pressurecompressed refrigerant through the reversing valve 122 and to theoutdoor heat exchanger 114, where the refrigerant may transfer heat toan airflow that is passed through and/or into contact with the outdoorheat exchanger 114 by the outdoor fan 118. After exiting the outdoorheat exchanger 114, the refrigerant may flow through and/or bypass theoutdoor metering device 120, such that refrigerant flow is notsubstantially restricted by the outdoor metering device 120. Refrigerantgenerally exits the outdoor metering device 120 and flows to the indoormetering device 112, which may meter the flow of refrigerant through theindoor metering device 112, such that the refrigerant downstream of theindoor metering device 112 is at a lower pressure than the refrigerantupstream of the indoor metering device 112. From the indoor meteringdevice 112, the refrigerant may enter the indoor heat exchanger 108. Asthe refrigerant is passed through coil 109 of the indoor heat exchanger108, heat may be transferred to the refrigerant from an airflow that ispassed through and/or into contact with the indoor heat exchanger 108 bythe indoor fan 110. Refrigerant leaving the indoor heat exchanger 108may flow to the reversing valve 122, where the reversing valve 122 maybe selectively configured to divert the refrigerant back to thecompressor 116, where the refrigeration cycle may begin again.

To operate the HVAC system 100 in the so-called heating mode, thereversing valve 122 may be controlled to alter the flow path of therefrigerant, the indoor metering device 112 may be disabled and/orbypassed, and the outdoor metering device 120 may be enabled. In theheating mode, refrigerant may flow from the compressor 116 to the indoorheat exchanger 108 through the reversing valve 122, the refrigerant maybe substantially unaffected by the indoor metering device 112, therefrigerant may experience a pressure differential across the outdoormetering device 120, the refrigerant may pass through the outdoor heatexchanger 114, and the refrigerant may re-enter the compressor 116 afterpassing through the reversing valve 122. Most generally, operation ofthe HVAC system 100 in the heating mode reverses the roles of the indoorheat exchanger 108 and the outdoor heat exchanger 114 as compared totheir operation in the cooling mode.

Referring now to FIG. 2 , a schematic diagram of an air circulation path200 of the HVAC system 100 of FIG. 1 is shown according to an embodimentof the disclosure. It will be appreciated that while three zones 202,204, 206 are shown, any number of zones may be present in an indoor areaor structure 201. Where present, the plurality of zones may beconditioned independently or together in one or more groups. The aircirculation path 200 of the HVAC system 100 may generally comprise afirst zone supply duct 208, a second zone supply duct 210, a third zonesupply duct 212, a first zone return duct 214, a second zone return duct216, a third zone return duct 218, a main return duct 220, and a mainsupply duct 222. A plurality of zone dampers 224 may be optionallyprovided. The air circulation path 200 also passes through the indoorunit 102, which may include an indoor heat exchanger 108, indoor fan110, and an air filter 136. In some embodiments, the air filter 136 maybe remote from the indoor unit 102, positioned elsewhere along the mainreturn duct 220 or the zone return ducts 214, 216, 218. In oneembodiment, the air filter 136 is positioned adjacent to an inlet to thezone return ducts 214, 216, 218.

In operation, the indoor fan 110 may be configured to generate anairflow through the indoor unit 102 to deliver temperature conditionedair from an air supply opening in the indoor unit 102, through the mainsupply duct 222, and to each of the plurality of zones 202, 204, 206through each of the first zone supply duct 208, the second zone supplyduct 210, and the third zone supply duct 212, respectively.Additionally, each of the first zone supply duct 208, the second zonesupply duct 210, and the third zone supply duct 212 may optionallycomprise a zone damper 224 that regulates the airflow to each of thezones 202, 204, 206. In some embodiments, the zone dampers 224 mayregulate the flow to each zone 202, 204, 206 in response to atemperature or humidity sensed by at least one temperature sensor and/orhumidity sensor carried by at least one of the system controller 106, azone thermostat 158, and a zone sensor 160.

Air from each zone 202, 204, 206 may return to the main return duct 220through each of the first zone return duct 214, the second zone returnduct 216, and the third zone return duct 218. From the main return duct220, air may return to the indoor unit 102 through an air return openingin the indoor unit 102. Air entering the indoor unit 102 through the airreturn opening may then be conditioned for delivery to each of theplurality of zones 202, 204, 206 as described above. Circulation of theair in this manner may continue repetitively until the temperatureand/or humidity of the air within the zones 202, 204, 206 conforms to atarget temperature as required by at least one of the system controller106, the zone thermostat 158, and/or the zone sensor 160.

To operate the HVAC system 100 in the so-called fan only mode, indoorfan 110 of indoor unit 102 may be operated to circulate air to theplurality of zones 202, 204, 206 of indoor area 201. When HVAC system100 is operated in the fan only mode, compressor 116 of outdoor unit 104may not be operated so that refrigerant is not circulated through indoorheat exchanger 108. Thus, when HVAC system 100 is operated in the fanonly mode, air may be circulated to the plurality of zones 202, 204, 206of indoor area 201 without conditioning the air via transferring heatbetween the air and refrigerant circulated through indoor heat exchanger108.

During the operation of HVAC system 100 in any of the cooling, heating,and fan only modes, circulation of air to the plurality of zones 202,204, and 206 of indoor area 201 by indoor fan 110 produces an externalstatic pressure (ESP) across indoor unit 102 defined by a differencebetween a supply static pressure of air circulated through main supplyduct 222 and a return static pressure of air circulating through mainreturn duct 220. Airflow and ESP produced by indoor fan 110 may beestimated by continuously measuring motor speed and torque of the motorof indoor fan 110.

Particularly, components of indoor unit 102 including indoor heatexchanger 108 and indoor fan 110 may be housed within a cabinet to forma self-contained air handling unit (AHU). Prior to installation ofindoor unit 102 at structure 201, the AHU of indoor unit 102 (or anotherAHU similar in configuration to the AHU of indoor unit 102) may betested at an air plenum test facility at a range of known airflows andESPs (i.e., independently measured by equipment of the test facility) tothereby create AHU maps correlating airflow and ESP of the AHU withmotor speed and torque of the indoor fan 110 of the AHU. For example, afirst AHU map may include airflow along an X-axis thereof, motor power(which may be calculated from a measured motor torque) along a Y-axisthereof, and a plurality of curves each corresponding to a fixed motorspeed. In this manner, airflow may be “looked-up” from the AHU map froma known motor speed and torque. A second AHU map may include airflowalong an X-axis thereof, ESP along a Y-axis thereof, and a plurality ofcurves each corresponding to a fixed motor speed, from which the ESP maybe looked-up given the known motor speed and airflow (determined fromthe first AHU map).

The AHU maps created during testing may be stored in the memory of thesystem controller 106. In this manner, system controller 106 of HVACsystem 100 may apply measured motor speed and torque values communicatedto system controller 106 from indoor fan controller 142 to the AHU mapsstored in the memory of system controller 106 to thereby determine orlook-up an estimated airflow and an estimated ESP provided by the indoorfan 110 corresponding to the measured motor speed and torque of theindoor fan 110.

Referring now to FIGS. 1-3 , a method 300 of determining a condition ofan air filter or cleaner of a climate control system is shown in FIG. 3. In some embodiments, method 300 may be practiced with HVAC system 100while HVAC system 100 is operated in the fan only mode as previouslydescribed above (see e.g., FIGS. 1, 2 ). Thus, in describing thefeatures of method 300, continuing reference will made to the HVACsystem 100 shown in FIGS. 1, 2 ; however, it should be appreciated thatembodiments of method 300 may be practiced with other systems,assemblies, and devices.

Generally speaking, method 300 includes comparing a calculated ormodeled ESP value (e.g., a calculated ESP value of the HVAC system 100shown in FIGS. 1, 2 ) with a baseline ESP value (which is alsocalculated or modeled) obtained with a clean air filter installed in theclimate control system. Method 300 may also generally include providinga user of the climate control system (e.g., a homeowner and/or systeminstaller of the HVAC system 100) with an alert to the user of theclimate control system that the air filter needs to be serviced (e.g.,cleaned or replaced) based on the comparison between the calculated ESPvalue and the baseline ESP value. As will be described in more detailbelow, performance of some or all of the steps of method 300 may becyclical or repeated during the lifetime of the climate control systemso as to continually monitor a condition (e.g., fouling) of the airfilter of the climate control system and to ensure that the air filteris timely serviced once fouled.

Initially, method 300 includes receiving confirmation from a user of aclimate control system that a clean air filter is installed in theclimate control system at block 302. In some embodiments, block 302 maycomprise a homeowner providing a user input to the I/O unit 107 of HVACsystem 100 that a clean air filter 136 is installed, for instance, atthe inlet of indoor unit 102 of HVAC system 100, or, in otherembodiments, at other locations remote from indoor unit 102. Forexample, the homeowner may provide the user input to I/O unit 107following the replacement of a fouled air filter 136 with a clean airfilter 136. In some embodiments, block 302 may comprise an installer ofHVAC system 100 providing a user input to the I/O unit 107 following thecommissioning of HVAC system 100. The user input provided to the I/Ounit 107 by the user of HVAC system 100 may be communicated to thesystem controller 106 of HVAC system 100. Alternatively, confirmationfrom the user as described in block 302 may be indirect. For example, acommissioning process of the HVAC system 100 may automatically provide asignal indicative of a clean air filter.

Method 300 also includes conducting an active filter test to obtain thebaseline ESP value at bracket 304, where the active filter testcomprises the execution of blocks 306-314 of method 300. Generallyspeaking, the active filter test defined by blocks 306-314 includesoperating the climate control system in the fan only mode without ademand for heating or cooling to generate data (including blocks 306,308, and 310) and performing calculations on the generated data(including blocks 312, 314) to obtain a calculated ESP value of theclimate control system at a selected airflow which may be used, in someembodiments, for detecting fouling of an air filter of the climatecontrol system. In some embodiments, bracket 304 of method 300 maycomprise obtaining a baseline ESP value provided by the indoor fan 110of the HVAC system 100 shown in FIGS. 1, 2 at a predetermined selectedairflow provided by indoor fan 110 for detecting fouling of the airfilter 136 of the HVAC system 100. In some embodiments, the selectedairflow is programmed into the memory of system controller 106. In otherembodiments, the selected airflow is stored on a remote server ofcommunication network 132. In certain embodiments, the selected airflowmay be entered into system controller 106 or communication network 132by the installer of HVAC system 100. In other embodiments, the selectedairflow is preprogrammed into system controller 106 as part of theprocess for manufacturing system controller 106. The selected airflowmay be a fraction (e.g., 50%-100%) of a maximum airflow that may beprovided by the indoor fan 110 that is sufficiently large such thatfouling of air filter 136 may result in a detectable increase in ESPprovided by indoor fan 110 at the selected airflow relative to thebaseline ESP value at the selected airflow.

As will be described further herein, conducting an active filter test,including the active filter test to obtain the baseline ESP value atbracket 304, includes placing a climate control system in an idle modeat block 306, continuously increasing a speed of an indoor fan of theclimate control system at block 308, collecting estimated airflow andESP values at periodic intervals for a predetermined test period atblock 310, obtaining estimated airflow start values and estimated ESPstart values, and estimated airflow end values and estimated ESP endvalues from the collected estimated airflow and ESP values at block 312;and obtaining a calculated ESP value at a selected airflow normalized bya maximum airflow that may be provided by the indoor fan at block 314.Thus, unlike a passive filter test where estimated airflow and ESPvalues are collected passively as the climate control system is in aheating or cooling mode to conform a temperature and/or humidity of anindoor space to a target temperature and/or humidity, in the activefilter test the climate control system is first placed in an idle modeand then airflow and ESP values are collected as the speed of an indoorfan of the climate control system is continuously increased or ramped upfrom zero (corresponding to the idle mode of the climate controlsystem). As described above, initially the active filter testcorresponding to bracket 304 of method 300 includes placing a climatecontrol system into an idle mode at block 306. In some embodiments,block 306 of method 300 may comprise placing HVAC system 100 shown inFIGS. 1, 2 into an idle mode where indoor fan 110 of HVAC system 100remains idle and air is not circulated along the air circulation path200 shown in FIG. 2 . The compressor 116 is also inactive during theidle mode such that refrigerant is not actively being circulated throughthe heat exchanger 108. In some embodiments, block 306 of method 300 maybe initiated by a user of HVAC system 100. For example, a homeowner mayprovide an input to the I/O unit 107 of HVAC system 100 commandingsystem controller 106 to initiate block 306 of method 300. In anotherexample, a system installer of HVAC system 100 may provide an input todevice 130 that is communicated to system controller 106 viacommunication network 132 which commands control system 106 to initiateblock 306 of method 300. In some embodiments, block 306 of method 300may comprise opening all zone dampers of a structure or indoor area, ifpresent. For example, block 306 may comprise opening each of theplurality of zone dampers 224 of the indoor area 201 shown in FIG. 2 .

As described above, method 300 also includes continuously increasing aspeed of an indoor fan of the climate control system at block 308. Insome embodiments, block 308 of method 300 may comprise transmitting amaximum airflow command from system controller 106 of HVAC system 100 tothe indoor fan controller 142 such that a speed and an airflow producedby indoor fan 110 continuously increases from zero (corresponding to theidle mode of HVAC system 100) towards a maximum airflow that may beprovided by the indoor fan 110. Additionally, block 308 may compriseplacing HVAC system 100 into the fan only mode.

With the speed of the indoor fan continuously increasing, method 300proceeds by collecting estimated airflow and estimated ESP values atperiodic intervals as the speed and airflow produced by the indoor fanincreases at block 310. In some embodiments, block 310 of method 300comprises collecting estimated airflow and ESP values of the indoor unit102 of HVAC system 100 as the speed and airflow produced by indoor fan110 of HVAC system 100 increases. For example, system controller 106 maycollect estimated airflow and estimated ESP values by continuouslymeasuring motor speed and torque of indoor fan 110 and estimating theestimated airflow and ESP values from the measured motor speed andtorque using AHU maps stored in the memory of system controller 106 asdescribed above. Each periodic interval may be approximately fiveseconds in duration, however, the duration of each periodic interval mayvary.

Referring briefly to FIG. 4 , an exemplary estimated airflow-ESP chart370 is shown that illustrates airflow in cubic feet per minute (CFM) onan X-axis thereof and ESP in inches of H₂O and a Y-axis thereof. Circles372 of estimated airflow-ESP chart 370 represent measured airflow andESP values obtained at block 310 of the method 300 shown in FIG. 3 . Asindicated in estimated airflow-ESP chart 370, estimated ESP increaseswith increasing airflow produced by the indoor fan of the climatecontrol system, with the first non-zero estimated ESP value occurring atan airflow of approximately 600 CFM. Estimated airflow-ESP chart 370serves to illustrate the general behavior of estimated airflow andmeasured ESP values obtained at block 310, and the estimated airflow andESP values collected at block 310 of method 300 may vary significantlyfrom those shown in FIG. 4 .

Referring again to FIGS. 1-3 , as estimated airflow and ESP values arecollected, a fitted ESP function is determined from the collectedestimated airflow and ESP values at block 312 of method 300. In someembodiments, block 312 of method 300 includes determining ESP andairflow or airflow rate start (ESP_(start) and, Airflow_(start),respectively) values and ESP and airflow or airflow rate end (ESP_(end)and, Airflow_(end), respectively) values used to determine the slope andintercept of the fitted ESP function, as will be described furtherherein.

The ESP_(start) and Airflow_(start) values may be determined byidentifying the first non-zero estimated airflow value collected atblock 310, and saving the third estimated non-zero airflow value as theAirflow_(start) value. For example, if the first non-zero estimatedairflow data is identified at the n periodic interval, then theestimated airflow data at the n+2 periodic interval may be saved as theAirflow_(start) value; however, in other embodiments, the estimatedairflow data at the n+1 n+4, etc., may comprise the Airflow_(start)value. Similarly, block 312 may comprise saving the third estimated ESPvalue following the identified first non-zero estimated airflow value asthe ESP_(start) value.

The ESP_(end) and Airflow_(end) values may be determined by identifyingthe emergence of a pseudo-steady state maximum for the estimated airflowand estimated ESP values collected at block 310 and saving thepseudo-steady state maximum estimated airflow and estimated ESP valuesas the Airflow_(end) value and the ESP end value. In some embodiments,the pseudo-steady state maximum estimated airflow and estimated ESPvalues may be determined via a comparison to a moving or rolling averageof estimated ESP values. For example, a predetermined number (e.g., fourneighboring estimated ESP values in this example) of neighboringestimated ESP values may be averaged to determine a first rollingaverage of estimated ESP values, and the first rolling average may becompared to the estimated ESP value collected immediately prior (the“first prior estimated ESP value”) to the collection of the fourestimated ESP values defining the first rolling average. In thisexample, the first prior estimated ESP value is determined to be thepseudo-steady state maximum estimated ESP value if the first priorestimated ESP value is less than the first rolling average. If the firstprior estimated ESP value is less than the first rolling average, thenthe process continues by substituting the first prior estimated ESPvalue with a second prior estimated ESP value comprising the estimatedESP value that was collected first of the four estimated ESP valuesdefining the first rolling average, and determining a second rollingaverage by averaging the next four estimated ESP values that immediatelyfollow the second prior estimated ESP value. The second prior estimatedESP value may then be compared with the second rolling average and so onand so forth. In other embodiments, other methodologies may be used todetermine the pseudo-steady state maximum airflow and ESP values ratherthan a rolling or moving average. For instance, the pseudo-steady statemaximum ESP value may be determined in response to a slope of theestimated ESP values over time being negative or less than apredetermined slope.

In some embodiments, the identified ESP_(start) and, Airflow_(start)values and the identified ESP_(end) and, Airflow_(end) values may eachbe saved into the memory of the system controller 106 of HVAC system100. In certain embodiments, the identified ESP_(start) andAirflow_(start) values and the identified ESP_(end) and Airflow_(end)values may each be transmitted to device 130 via communication network132. In some embodiments, once the ESP_(end) and Airflow_(end) valueshave been collected, the climate control system may return to normaloperation. For example, in some embodiments, following the collection ofthe ESP_(end) and Airflow_(end) values, HVAC system 100 may return tothe cooling or heating mode. Although the duration of the ramping of thespeed of the indoor fan of the climate control system at block 308 isnot fixed or predefined, in most applications only a few minutes (e.g.,two to three minutes) will be required for performing the active filtertest before the climate control system may be returned to normaloperation.

Once ESP_(start), Airflow_(end), ESP_(end) and, Airflow_(end) valueshave each been identified and saved, method 300 proceeds by obtaining acalculates ESP value at a selected airflow using the fitted ESP functionat block 314. Given that bracket 304 of method 300 is executedimmediately following the execution of block 302, the calculated ESPvalue obtained at block 314 of bracket 304 comprises a baseline ESPvalue of the climate control system obtained with a clean air filter(e.g., air filter 136 of HVAC system 100) installed in the climatecontrol system.

In some embodiments, the selected airflow is normalized by a maximumairflow that may be provided by the indoor fan of the climate controlsystem at block 314. The maximum airflow of the indoor fan of theclimate control system may be predetermined and based upon theconfiguration of the indoor fan and climate control system, and thus,the maximum airflow may vary depending upon the configuration of the fanand climate control system. Without being limited to this or any othertheory, the calculated ESP value may be obtained by the followingcomputation, where the calculated ESP value obtained at block 314 isrepresented by ESP_(calculated), the maximum airflow is represented byAirflow_(maximum), and A, B are constants which will be describedfurther herein:

$\begin{matrix}{{ESP_{ca{lculated}}} = {{A\left( \frac{{Airflow}_{select}}{{Airflow}_{\max{imum}}} \right)} + B}} & (1)\end{matrix}$

Not intending to be limited to this or any other theory, the constant Aof equation (1) above may be obtained by the following computation:

$\begin{matrix}{A = \frac{{ESP_{start}} - {ESP_{end}}}{\frac{{Airflow}_{start}}{{Airflow}_{target}} - \frac{{Airflow}_{end}}{{Airflow}_{target}}}} & (2)\end{matrix}$

Not intending to be limited to this or any other theory, the constant Bof equation (1) above may be obtained by the following computation:

$\begin{matrix}{B = {{ESP_{end}} - \frac{{Airflow}_{end}}{{Airflow}_{target}}}} & (3)\end{matrix}$

In some embodiments, the fitted ESP function of block 312 comprisesEquation (1) above while constant A defines a slope of the fitted ESPfunction and constant B defines an intercept of the fitted ESP function.Thus, block 314 of method 300 may include solving the fitted ESPfunction (comprising Equation (1) above) determined at block 312 byentering constants A, B, and the selected airflow (represented byESP_(calculated) in equation (1) above) into Equation (1). Thus, theAirflow_(start), Airflow_(end) values and the ESP_(start), ESP_(end)values bound or delimit the estimated airflow and ESP values used toobtain the calculated ESP value. The selected airflow may comprise apredetermined percentage of the maximum airflow. As described above, theselected airflow may be a fraction (e.g., 50%-100%) of the maximumairflow that may be provided by the indoor fan 110 that is substantiallylarge enough to create an appreciable pressure drop across air filter136 but that is less than the maximum airflow given that the motor ofindoor fan 110 may be torque-limited or otherwise prevented fromachieving a full 100% of the maximum airflow. In some embodiments, theselected airflow is approximately 80% of the maximum airflow; however,in other embodiments, the selected airflow of a given target airflow mayvary. For example, in an embodiment where the selected airflow comprises80% of the maximum airflow and the maximum airflow is approximately1,200 CFM, the selected airflow may comprise 80% of the maximum airflowor approximately 960 CFM.

Referring briefly to FIG. 5 , an exemplary fitted airflow-ESP chart 380is shown that illustrates airflow in CFM on an X-axis thereof and ESP ininches of H₂O on a Y-axis thereof. In addition to the estimated airflowand ESP values indicated by circles 372, fitted airflow-ESP chart 380comprises triangles 382 which represent calculated ESP values at a rangeof selected airflows. Thus, each triangle 382 of fitted airflow-ESPchart 380 is obtained from equations (1)-(3) above for varying selectedairflows. Thus, given that the ESP_(start) value of equations (1)-(3)comprises the third measured non-zero airflow value, two non-zeroairflow circles 372 are shown on fitted airflow-ESP chart 380 prior tothe first or lowest non-zero airflow triangle 382. Also as illustratedin fitted airflow-ESP chart 380, the selected airflow of any of thecalculated ESP values represented by triangles 382 need not comprise oneof the measured airflows obtained at block 310 of the method 300 shownin FIG. 3 . Instead, the selected airflow on which the calculated ESPvalue is obtained may comprise any airflow between the Airflow_(start)value and the Airflow_(end) value. Fitted airflow-ESP chart 380 servesto illustrate the general behavior of the calculated ESP values forvarying selected airflows, and the calculated ESP value obtained atblock 314 of the method 300 shown in FIG. 3 may vary significantly fromthose shown in FIG. 5 .

Still referring to FIGS. 1-3 , method 300 also includes conducting anactive filter test after a predetermined period of time from conductingthe previous active filter test to obtain a calculated ESP value atblock 316. In some embodiments, block 316 comprises performing the stepsdefined by blocks 306-314 described above after the predetermined periodof time from conducting the previous active filter test at bracket 304of method 300 has elapsed. Thus, in some embodiments, block 316 ofmethod 300 comprises obtaining, instead of the baseline ESP value, acalculated ESP value of the HVAC system 100 shown in FIGS. 1, 2 at thepredefined selected airflow. Thus, the steps defined by blocks 306-314may be performed to obtain both the baseline ESP value obtained atbracket 304 of method 300 and the calculated ESP value obtained at block316 of method 300. In this manner, the active filter test defined byblocks 306-314 of method 300 may be used to detect fouling of an airfilter of the climate control system.

The predetermined period of time between the conducting of the activefilter test for obtaining the baseline ESP value and the conducting theactive filter test to obtain the calculated ESP value may beapproximately one month for indoor areas (e.g., indoor area 201 shown inFIG. 2 ) comprising a residential home; however, the duration of thepredetermined period of time may vary depending upon the configurationof the structure and climate control system. For example, thepredetermined time period may vary between one week and two to threemonths depending upon the application; however, the predetermined timeperiod will be at least on week or greater in length in order tominimize disruption to the normal operation of the climate controlsystem.

Method 300 further includes determining whether the calculated ESP value(obtained at block 316) is a maximum percentage greater than thebaseline ESP value (obtained at block 304) at block 318. For instance,without being limited to this or any other theory, the percentageincrease from the baseline ESP value to the calculated ESP value may becalculated (or estimated) by the following computation, where thebaseline ESP value obtained via bracket 304 of method 300 is representedby ESP_(base) and the calculated ESP value obtained at block 316 isrepresented by ESP_(calculated):

$\begin{matrix}{{Percentage}{Increase}{= {\left( \frac{{ESP_{calculated}} - {ESP_{base}}}{ESP_{base}} \right)100}}} & (4)\end{matrix}$

Once the percentage increase from the baseline ESP value to thecalculated ESP value is calculated, block 318 of method 300 may includedetermining whether the calculated percentage increase is equal to orgreater than a predetermined maximum percentage increase or thresholdvalue, which would be indicative of fouling of the air filter of theclimate control system (e.g., air filter 136 of HVAC system 100). Insome embodiments, the maximum percentage increase is programmed into thememory of the system controller 106 of HVAC system 100. In otherembodiments, the maximum percentage increase is stored on a remoteserver of communication network 132. In certain embodiments, the maximumpercentage increase may be entered into system controller 106 orcommunication network 132 by the installer of HVAC system 100. In otherembodiments, the maximum percentage increase is preprogrammed intosystem controller 106 as part of the process for manufacturing systemcontroller 106. The maximum percentage increase is sized to indicate apressure drop of approximately 50% across the air filter of the climatecontrol system, a value indicative of fouling of the air filter.However, a 50% pressure drop across the air filter of the climatecontrol system may register as less than a 50% increase in ESP providedby an indoor fan of the climate control system given that the increasein ESP provided by the indoor fan reflects pressure losses not onlyacross the air filter, but across an entire air circulation path (e.g.,air circulation path 200 shown in FIG. 2 ) of the climate controlsystem, where pressure losses across the air filter only contribute aportion to the entirety of pressure losses in the climate controlsystem. Therefore, in some embodiments the maximum percentage increasemay be approximately 30% to reflect a pressure loss across the airfilter of approximately 50%; however, the maximum percentage increase ofblock 318 of method 300 may vary depending on the particularapplication.

If it is determined that the percentage increase is less than thepredetermined maximum percentage increase (i.e., the determination atblock 318 is “No”), method 300 may return again to block 316 where anactive filter test is conducted by performing the steps defined byblocks 306-314 after the predetermined period of time has passed fromconducting the preceding active filter test to obtain a new or secondcalculated ESP value. The newly obtained calculated ESP value may thenbe compared with the baseline ESP value at block 318 of method 300 todetermine whether the percentage increase from the baseline ESP value tothe newly obtained calculated ESP value is equal to or greater than thepredetermined maximum percentage increase.

If it is determined that the percentage increase is equal to or greaterthan the predetermined maximum percentage increase (i.e., thedetermination at block 318 is “Yes”), method 300 may proceed to block320 where an alert is produced to a user of the climate control systemto service the air filter. For instance, in an example where the maximumpercentage increase is 30%, if a baseline ESP value of 0.7 (inches ofH₂O) is obtained at a selected airflow of 80% of a maximum airflow of1,200 CFM of an indoor fan of a climate control system, and a calculatedESP value of 1.0 (inches of H₂O) is obtained at the selected airflow of80% of the maximum airflow of 1,200 CFM, then an alert would be producedgiven that the 43% percentage increase between the baseline ESP valueand calculated ESP value in this example is greater than 30% maximumpercentage increase.

Servicing the air filter of the climate control system may comprisereplacing or cleaning the air filter. In some embodiments, block 320 ofmethod 300 may comprise producing a visual alert on I/O unit 107 of HVACsystem 100 to inform the homeowner that air filter 136 of HVAC system100 needs to be serviced. In certain embodiments, block 320 may comprisecommunicating the alert to the device 130 of HVAC system 100 viacommunication network. For example, device 130 may comprise a serveraccessible by a system installer of HVAC system 100 or a technicianequipped to service HVAC system 100, and in this manner the systeminstaller or technician may be informed of the required servicing of airfilter 136 by accessing device 130. Once the air filter of the climatecontrol system has been serviced (i.e., cleaned or replaced), method 300may return to block 302 where confirmation is received from the user ofa climate control system that a clean air filter is installed in theclimate control system.

Still referring to FIGS. 1-3 , through use of the systems and methodsdescribed herein (e.g., HVAC system 100, method 300, etc.), the foulingof an air filter or cleaner of a climate control system may beaccurately and timely detected such that the fouled air filter may bepromptly replaced by a user of the climate control system. Specifically,a climate control system for an indoor space (e.g., HVAC system 100 andindoor area 201) may be operated by operating an indoor fan (e.g.,indoor fan 110) of the climate control system to produce an airflowthrough the indoor space, obtaining a baseline ESP value (e.g., thebaseline ESP value obtained at bracket 304 of method 300) of the climatecontrol system based on a first plurality of estimated airflow valuesand a first plurality of estimated ESP values (e.g., airflow values andESP values obtained at the block 310 of bracket 304 of method 300),obtaining a calculated ESP value of the climate control system based ona second plurality of estimated airflow values and a second plurality ofestimated ESP values (e.g., airflow values and ESP values obtained atblock 316 of method 300), and comparing the calculated ESP value to thebaseline ESP value to determine a condition of an air filter of theclimate control system (e.g., determination made at block 318 of method300).

Additionally, a controller (e.g., system controller 106 of HVAC system100) may comprise a non-transitory machine-readable medium includinginstructions that, when executed by a processor of the controller, causethe processor to operate the indoor fan of the climate control system toproduce the airflow through the indoor space, obtain the baseline ESP ofthe climate control system based on the first plurality of estimatedairflow values and the first plurality of estimated ESP values, obtainthe calculated ESP value of the climate control system based on thesecond plurality of estimated airflow values and the second plurality ofestimated ESP values, and compare the calculated ESP value to thebaseline ESP value to determine the condition of an air filter of theclimate control system.

By obtaining the baseline ESP value and the calculated ESP value of theclimate control system based on a plurality of estimated airflow valuesand a plurality of estimated ESP values, respectively, the duration ofthe active filter test (e.g., as defined by blocks 306-314 of method300) used to obtain the baseline ESP value and the calculated ESP valuemay be minimized so that the climate control may be returned to normaloperation as quickly as possible, thereby maximizing the comfort of thehomeowner. Particularly, estimated airflow and ESP values are collectedas the speed and airflow produced by the indoor fan increases from anidle mode, and the collection of estimated airflow and ESP values may beterminated as soon as a pseudo-steady state airflow and a pseudo-steadystate ESP are achieved. Thus, the collection of estimated airflow andESP values begins as soon as possible during the active filter test(i.e., promptly after they become greater than zero) and is terminatedas soon as possible (i.e., when a pseudo-steady state is achieved),thereby minimizing the amount of time required for collecting theestimated airflow and ESP values upon which the baseline ESP value andcalculated ESP value are based. By minimizing the amount of timerequired for collecting the estimated airflow and ESP values upon whichthe baseline ESP value and calculated ESP value are based, the overalltime required for conducting the active filter test may in-turn beminimized.

Further, by obtaining and comparing a calculated or modeled ESP with abaseline ESP value that is also calculated or modeled, a more accuratedetermination of whether an air filter of a climate control system maybe made. Particularly, each calculated ESP value is based upon aplurality of “fitted” estimated airflow and ESP values rather than asingle estimated ESP at a single estimated airflow or a plurality ofestimated ESPs that are simply averaged together. By basing thecomparison in calculated ESP value and baseline ESP value upon aplurality of estimated airflow and ESP values that are fitted as part ofa model (e.g., the model described in equations (1)-(3) above), errorsassociated with any particular estimated airflow and/or ESP value may bemitigated.

While exemplary embodiments have been shown and described, modificationsthereof can be made by one skilled in the art without departing from thescope or teachings herein. The embodiments described herein areexemplary only and are not limiting. Many variations and modificationsof the systems, apparatus, and processes described herein are possibleand are within the scope of the disclosure. Accordingly, the scope ofprotection is not limited to the embodiments described herein, but isonly limited by the claims that follow, the scope of which shall includeall equivalents of the subject matter of the claims. Unless expresslystated otherwise, the steps in a method claim may be performed in anyorder. The recitation of identifiers such as (a), (b), (c) or (1), (2),(3) before steps in a method claim are not intended to and do notspecify a particular order to the steps, but rather are used to simplifysubsequent reference to such steps.

What is claimed is:
 1. A method of operating a climate control systemfor an indoor space, the method comprising: (A) conducting a firstactive filter test on the climate control system at a first time, theclimate control system being installed at a given location and includinga given air filter during the first active filter test, the first activefilter test including: (a) increasing, from idle, a speed of an indoorfan of the climate control system to increase an airflow through theindoor space, (b) determining a first fitted external static pressure(ESP) function from a first plurality of airflow values and a firstplurality of ESP values, and (c) obtaining a baseline ESP value of theclimate control system from the first fitted ESP function; and (B)conducting a second active filter test on the climate control system ata second time, the climate control system being installed at the givenlocation and including the given air filter during the second activefilter test, the second time being at least one week after the firsttime, the second active filter test including: (d) determining a secondfitted ESP function from a second plurality of airflow values and asecond plurality of ESP values, (e) obtaining a first calculated ESPvalue of the climate control system from the second fitted ESP function,and (f) comparing the first calculated ESP value to the baseline ESPvalue to determine a condition of an air filter of the climate controlsystem.
 2. The method of claim 1, wherein (d) comprises: (d1)determining an airflow start value and an ESP start value at a firstairflow rate; and (d2) determining an airflow end value and an ESP endvalue at a second airflow rate which is greater than the first airflowrate.
 3. The method of claim 2, wherein (d1) comprises identifying afirst non-zero airflow of the first plurality of airflow values.
 4. Themethod of claim 2, wherein (d2) comprises identifying when apseudo-steady state maximum airflow and a pseudo-steady state maximumESP have been achieved.
 5. The method of claim 1, wherein (f) comprises:(f1) determining a percentage increase in the first calculated ESP valueover the baseline ESP value; and (f2) comparing the determinedpercentage increase with a predetermined maximum percentage increase. 6.The method of claim 1, further comprising: (g) issuing an alert to auser of the climate control system to service the air filter in responseto the determined percentage increase being greater than thepredetermined maximum percentage increase.
 7. The method of claim 1,wherein the first and the second active filter test include operatingthe climate control system in a fan only mode.
 8. The method of claim 1,further comprising: (g) measuring a speed and a torque of a motor of theindoor fan, wherein the first plurality of airflow values, the secondplurality of airflow values, the first plurality of ESP values, and thesecond plurality of ESP values are estimated from the measured speed andthe measured torque of the motor of the indoor fan.
 9. The method ofclaim 1, further comprising: (C) conducting a third active filter teston the climate control system at a third time, the climate controlsystem being installed at the given location and including the given airfilter during the third active filter test, the third time being atleast one week after the second time, the third active filter testincluding: (g) determining a third fitted ESP function from a thirdplurality of airflow values and a third plurality of ESP values, (h)obtaining a second calculated ESP value of the climate control systemfrom the third fitted ESP function, and (i) comparing the secondcalculated ESP value to the baseline ESP value to determine thecondition of the air filter of the climate control system.
 10. A climatecontrol system for an indoor space, the climate control systemcomprising: an indoor fan configured to produce an airflow through theindoor space; an air filter configured to filter contaminants in theairflow produced by the indoor fan; a controller to be coupled to theindoor fan, wherein the controller is configured to: conduct a firstactive filter test on the climate control system at a first time, theclimate control system being installed at a given location and includingthe air filter during the first active filter test, the first activefilter test including: increasing, from idle, a speed of the indoor fanof the climate control system to increase the airflow through the indoorspace, determining a first fitted external static pressure (ESP)function from a first plurality of airflow values and a first pluralityof ESP values, and obtaining a baseline ESP value of the climate controlsystem from the first fitted ESP function; conduct a second activefilter test on the climate control system at a second time, the climatecontrol system being installed at the given location and including theair filter during the second active filter test, the second time beingat least one week after the first time, the second active filter testincluding: determining a second fitted ESP function from a secondplurality of airflow values and a second plurality of ESP valuescollected by the controller at least one week after the first pluralityof airflow values and the first plurality of ESP values are collected bythe controller; obtaining a first calculated ESP value of the climatecontrol system from the second fitted ESP function; and comparing thefirst calculated ESP value to the baseline ESP value to determine acondition of the air filter of the climate control system.
 11. Theclimate control system of claim 10, wherein the controller is configuredto enter a selected airflow into the second fitted ESP function, andwherein the selected airflow is normalized by a maximum airflow of theindoor fan in the second fitted ESP function.
 12. The climate controlsystem of claim 10, wherein: at least one of the first plurality ofairflow values and the second plurality of airflow values are bounded byan airflow start value at a first airflow rate determined by thecontroller and an airflow end value at a second airflow rate determinedby the controller which is greater than the first airflow rate; and atleast one of the first plurality of ESP values and the second pluralityof ESP values are bounded by an ESP start value at the first airflowrate and an ESP end value at the second airflow rate.
 13. The climatecontrol system of claim 12, wherein the controller is configured todetermine a percentage increase in the first calculated ESP value overthe baseline ESP value and compare the determined percentage increasewith a predetermined maximum percentage increase.
 14. The climatecontrol system of claim 13, wherein the controller is configured toissue an alert to a user of the climate control system to service theair filter in response to the determined percentage increase beinggreater than the predetermined maximum percentage increase.
 15. Theclimate control system of claim 10, wherein the controller is configuredto: measure a speed and a torque of a motor of the indoor fan; andestimate the first plurality of airflow values, the second plurality ofairflow values, the first plurality of ESP values, and the secondplurality of ESP values from the measured speed and the measured torqueof the motor of the indoor fan.
 16. The climate control system of claim10, wherein the controller is configured to: conduct a third activefilter test on the climate control system at a third time, the climatecontrol system being installed at the given location and including thegiven air filter during the third active filter test, the third timebeing at least one week after the second time, the third active filtertest including: determining a third fitted ESP function from a thirdplurality of airflow values and a third plurality of ESP valuescollected by the controller, obtaining a second calculated ESP value ofthe climate control system from the third fitted ESP function, andcomparing the second calculated ESP value to the baseline ESP value todetermine the condition of the air filter of the climate control system.17. A non-transitory machine-readable medium including instructionsthat, when executed by a processor, cause the processor to: conduct afirst active filter test on the climate control system at a first time,the climate control system being installed at a given location andincluding a given air filter during the first active filter test, thefirst active filter test including: increasing, from idle, a speed of anindoor fan of the climate control system to increase an airflow throughthe indoor space; determining a first fitted external static pressure(ESP) function from a first plurality of airflow values and a firstplurality of ESP values; obtaining a baseline ESP value of the climatecontrol system from the first fitted ESP function; conduct a secondactive filter test on the climate control system at a second time, theclimate control system being installed at the given location andincluding the given air filter during the second active filter test, thesecond time being at least one week after the first time, the secondactive filter test including: determining a second fitted ESP functionfrom a second plurality of airflow values and a second plurality of ESPvalues collected by the controller at least one week after the firstplurality of airflow values and the first plurality of ESP values arecollected by the controller; obtaining a first calculated ESP value ofthe climate control system from the second fitted ESP value; andcomparing the first calculated ESP value to the baseline ESP value todetermine a condition of an air filter of the climate control system.18. The non-transitory machine-readable medium of claim 17, wherein: atleast one of the first plurality of airflow values and the secondplurality of airflow values are bounded by an airflow start value at afirst airflow rate determined by the controller and an airflow end valueat a second airflow rate determined by the controller which is greaterthan the first airflow rate; and at least one of the first plurality ofESP values and the second plurality of ESP values are bounded by an ESPstart value at the first airflow rate and an ESP end value at the secondairflow rate.
 19. The non-transitory machine-readable medium of claim17, wherein the instructions, when executed by a processor, cause theprocessor to: identify when a pseudo-steady state maximum airflow and apseudo-steady state maximum ESP have been achieved; determine apercentage increase in the first calculated ESP value over the baselineESP value and compare the determined percentage increase with apredetermined maximum percentage increase; and issue an alert to a userof the climate control system to service the air filter in response tothe determined percentage increase being greater than the predeterminedmaximum percentage increase.
 20. The method of claim 1, whereinconducting the second active filter test further includes increasing,from idle, a speed of an indoor fan of the climate control system toincrease an airflow through the indoor space.
 21. The method of claim 1,wherein the baseline ESP value corresponds to a selected airflow valuein the first fitted ESP function, wherein the calculated ESP valuecorresponds to the selected airflow value in the second fitted ESPfunction.
 22. The climate control system of claim 10, wherein the secondactive filter test further includes increasing, from idle, a speed of anindoor fan of the climate control system to increase an airflow throughthe indoor space.
 23. The climate control system of claim 10, whereinthe baseline ESP value corresponds to a selected airflow value in thefirst fitted ESP function, wherein the calculated ESP value correspondsto the selected airflow value in the second fitted ESP function.
 24. Thenon-transitory machine-readable medium of claim 17, wherein the secondactive filter test further includes increasing, from idle, a speed of anindoor fan of the climate control system to increase an airflow throughthe indoor space.
 25. The non-transitory machine-readable medium ofclaim 17, wherein wherein the baseline ESP value corresponds to aselected airflow value in the first fitted ESP function, wherein thecalculated ESP value corresponds to the selected airflow value in thesecond fitted ESP function.